The invention relates to an internal combustion engine for a handheld portable work apparatus such as a motor-driven chain saw, brushcutter, cutoff machine or the like. The invention is especially directed to a two-stroke engine.
In known internal combustion engines, and to provide a vibration-decoupled connection of the carburetor to an inlet opening for the air/fuel mixture, the carburetor is connected to the inlet opening with the aid of an intake stub of elastic material. The inlet opening is provided in the cylinder of the engine.
During the operation of the engine, the air/fuel mixture flows from the carburetor to the inlet opening and is deposited, in part, on the wall in the interior of the intake stub. The fuel, which is deposited in the intake stub, forms bubbles or collections of fuel depending upon the position of the work apparatus. The bubbles or collections of fuel are stochastically drawn by suction into the inlet opening when pivoting the work apparatus and can lead to an overenrichment of the air/fuel mixture. Especially at idle of the engine, this can lead to ignition misfires or even to standstill of the engine.
It is an object of the invention to improve a known internal combustion engine in such a manner that a uniform operation is possible.
The internal combustion engine of the invention includes a two-stroke engine for a portable handheld work apparatus including a motor-driven chain saw and cutoff machine. The engine includes: a cylinder having an inlet opening for receiving an air/fuel mixture; an intake stub through which the air/fuel mixture passes and wherein fuel can precipitate out of the air/fuel mixture during operation of the engine; the intake stub being made of elastic material and being mounted to conduct the air/fuel mixture into the inlet opening; a fuel collecting device for collecting the fuel precipitated in the intake stub; the fuel collecting device being delimited at least partially by the intake stub; and, a channel connecting the fuel collecting device to the cylinder.
The engine is provided with a fuel collecting device (especially at the intake stub) for uniformly conducting away fuel which deposits in the interior of the intake stub during operation of the engine. The fuel collecting device is mounted between the inlet opening and the carburetor viewed in the axial direction of the intake stub and is delimited at least partially by the intake stub. A channel is guided between an opening at the inlet opening at the cylinder and the fuel collecting device. The channel connects the fuel collecting device to the cylinder, that is, the crankcase. The channel conducts fluids from the fuel collecting device to the cylinder.
The inlet opening and the opening of the channel at the cylinder are controlled by the piston reciprocating in the cylinder during operation of the engine configured as a two-stroke engine. For this reason, cyclical underpressures are present at the inlet opening as well as in the channel itself. The underpressure is therefore present also in the channel and the fuel collecting device and effects a drawing in of the fuel, which collects in the fuel collecting device, into the cylinder or into the crankcase of the engine. In this way, during operation of the engine, a uniform conducting away of fuel is effected which deposits on the inner side of the wall of the intake stub. A uniform operation of the engine is thereby made possible.
The fuel collecting device can be configured in different ways, such as a collection space in the form of a recess in the intake stub. It can be practical to arrange the fuel collecting device in the proximity of the inlet opening and it is practical to configure the fuel collecting device as a collecting enclosure especially with respect to the technical manufacture of the intake stub. The collecting enclosure is delimited by a cylindrical outer surface at the inlet opening and a surface of the intake stub. It is practical to configure the collecting enclosure as an annular enclosure between the cylinder outer surface around the inlet opening and the intake stub to conduct away the deposited fuel from the total peripheral region in the interior of the intake stub.
A bellows-like thickening is provided on the intake stub in order to compensate longitudinal changes of the intake stub during operation of the engine. The thickening can expand the clear cross section of the intake stub in the region of the thickening. It is practical to provide the thickening interior space as a collecting device or collecting enclosure for fuel. To conduct away fuel deposited on the inner side of the intake stub, it can be practical to configure the fuel collecting stub in the form of openings which open in the interior of the intake stub and which are connected fluidly to the channel. The openings can be arranged as desired in the longitudinal direction or in the peripheral direction of the intake stub. It can be practical to allow the openings to open at spacings to each other sieve-like at one or several locations in the intake stub or partially in the intake stub and partially at the inlet opening at the cylinder.
In a preferred embodiment, the channel runs from the cylinder or crankcase interior in the intake stub of the cylinder below the inlet opening. The channel opens below the inlet opening into the cylinder or into the crankcase of the engine. In this way, the channel is emptied of collected fuel during operation of the engine because of the crankcase underpressure and then the inlet opening is cleared for the air/fuel mixture. In this way, fuel is conducted out of the fuel collecting device with each induction stroke. In dependence upon the spatial arrangement of the fuel collecting device and especially its arrangement in the axial direction of the intake stub, the channel opens directly at the cylinder outer surface into the fuel collecting device configured as a collecting enclosure or annular enclosure. If the fuel collecting device is in the form of a collecting device mounted axially from the cylinder outer surface at a spacing and is configured in the intake stub (as collection enclosure, thickening inner enclosure or openings preferably arranged sieve-like), then it is practical to lead the channel along the outer side of the intake stub to the collecting device. It can be practical to lead the channel in the wall of the intake stub or in the interior of the intake stub itself essentially in axial direction of the intake stub and to configure the channel as one piece with the intake stub from parts of the wall of the intake stub.
The channel as well as the intake stub itself is preferably cylindrically shaped. The channel has a significantly smaller inner diameter than the inner diameter of the intake stub. Preferably, the inner diameter of the channel is approximately ten times smaller than the inner diameter, especially the mean inner diameter, of the intake stub. With this constructive measure, a high flow velocity is provided in the channel and a reliable permanent removal of the fuel, which collects in the fuel collecting device, via the channel is ensured.
If, as a fuel collecting device, the thickening interior enclosure of the thickening at the intake stub is provided, then, in dependence upon the flow conditions during operation of the engine in the interior of the intake stub, it can be practical to arrange the thickening axially centered or in the proximity of the carburetor and/or cylinder end flange of the intake stub.
For effective supply of the deposited fuel into the thickening interior enclosure, which is charged with cyclical underpressure from the channel, it is practical to configure the clear width or the inner diameter of the intake stub (with reference to the flow direction of the air/fuel mixture in the intake stub) upstream of the thickening to be equal to or greater than downstream of the thickening. In addition, it is practical to lead the wall in the form of a ring-shaped section axially over the thickening on the inner side of the intake stub. In this way, an axially displaceable covering of the thickening interior enclosure results in the region of the thickening. Here, it is the object to extend the ring-shaped axial section beyond the length of the thickening and to provide this section as a lip in the intake channel. In this way, the expansion fold which the thickening forms is sealed off under specific operating conditions and yet an expansion and contraction of the expansion fold is not hindered.
The covering clears an annular gap to the interior space of the thickening with a corresponding axial displacement. In this way, fuel, which is precipitated onto the wall of the intake stub (especially in the region of the annular-shaped section), flows in the radial direction of the intake stub into the interior space of the thickening and, from there, the fuel is conducted away by the channel. This pumping away of the fuel takes place with the frequency of the engine and is not determined stochastically by the work technique of the operator. It can be practical to provide cutouts on the lip or annular-shaped edge of the annular-shaped section to facilitate the inflow of the precipitated fuel. With the cutouts, precipitated fuel can be conveyed continuously into the interior space of the thickening.
It can be practical to subdivide the channel to the fuel collecting device or to the interior space of the thickening into several branch channels. With this measure, fuel can be conducted away over the entire periphery of the thickening. With this measure, fuel is conducted away independently of the particular work position of the portable handheld work apparatus. In lieu of branching the channel into branch channels, it can be practical to lead several channels from the corresponding fuel collecting device into the cylinder.
In a preferred embodiment, a check valve is mounted in the channel which prevents fuel from being conveyed from the cylinder into the channel by an overpressure in the crankcase or in the cylinder. The check valve can be configured from a rubber membrane.